1. Field of the Invention
The present invention relates to a pulverized fuel combustion burner to be applied to a boiler of a thermal power plant or chemical plant, a furnace of a chemical plant or the like.
2. Related Art
A technique of the prior art will be described with reference to FIGS. 5(a)-(c). FIGS. 5(a) to 5(c) are side sections showing a construction of a pulverized fuel combustion burner schematically. FIGS. 5(a), 5(b) and 5(c) show the cases, respectively, in which a mixed flow of a pulverized fuel and carrier air is injected horizontally, in which the mixed flow is injected upwardly, and in which the mixed flow is injected downwardly.
Reference numeral 1 designates a primary air nozzle (also more simply referred to as the `primary nozzle`), and numeral 2 designates a second air nozzle arranged outside of the primary air nozzle 1. Numeral 3 designates a pulverized fuel supply pipe, and numeral 4 designates a combustion auxiliary fuel supply passage which is defined by the pulverized fuel supply pipe 3 and a windbox 5. The pulverized fuel supply pipe 3 communicates with the primary air nozzle 1, and its terminal end, and the combustion auxiliary air supply passage 4 communicates with the secondary air nozzle 2.
Reference numeral 10 designates a rich/lean flow separator which is arranged in the pulverized fuel supply pipe 3 so that a mixed flow 7 of the pulverized fuel and the carrier air, flowing through the pulverized fuel supply pipe 3, may impinge upon the rich/lean flow separator 10 and may be separated by the action of centrifugal force into a relatively rich flow 8 (as indicated by solid lines) to flow along the outer side and a lean flow 9 (as indicated by broken lines) to flow along the inner side.
Here, reference numeral 12 designates a clearance which is established between the furnace side end portion of the windbox 5 and the windbox side end portion of the secondary air nozzle 2 when the secondary air nozzle 2 is directed upward, as shown in FIG. 5(b), or downward, as shown in FIG. 5(c), by .theta. degrees.
Under ordinary operation, the mixed flow 7 of the pulverized fuel and the carrier air is guided through the pulverized fuel supply pipe 3 into the primary air nozzle 1 so that it is injected into the furnace. On the other hand, the combustion auxiliary air is guided through the combustion auxiliary air supply passage 4 into the secondary air nozzle 2 so that it is injected into the furnace.
In order to satisfy performances criteria for a low Nox combustion required from a combustion aspect, both the relatively rich and lean flows 8 and 9 of the pulverized fuel, as separated after the mixed flow 7 is separated by the action of the rich/lean flow separator 10, have to maintain a proper concentration distribution on a furnace side exit plane of the primary air nozzle 1.
Moreover, the combustion auxiliary air has to be injected as wholly as possible through the secondary air nozzle 2 into the furnace to thereby make an effective contribution to the combustion.
FIG. 5(a) shows the state in which the mixed flow 7 and the combustion auxiliary air are injected horizontally into the furnace. In this burner of the prior art, the injection direction of the mixed flow 7 and the combustion auxiliary air into the furnace can be changed upward or downward by directing the primary air nozzle 1 and the secondary air nozzle 2 upward or downward, respectively, as shown in FIGS. 5(b) and 5(c). As a result, the position of the flame to be maintained in the furnace can be moved upward or downward in the furnace to thereby adjust the gas temperature distribution in the furnace and the gas temperature at the furnace exit plane.
In the burner of the prior art thus far described, the mixed flow 7 of the pulverized fuel and carrier air can achieve the proper concentration distribution in the furnace side exit plane of the primary air nozzle 1 when it is injected horizontally into the furnace, as shown in FIG. 5(a). When the primary air nozzle I is directed upward or downward, respectively, as shown in FIG. 5(b) or 5(c), on the other hand, the relatively rich flow 8 of the pulverized fuel is biased, causing a problem in that the mixed flow 7 cannot establish the proper rich/lean distribution in the furnace side exit plane of the primary air nozzle 1 like the state shown in FIG. 5(a).
Moreover, the combustion auxiliary air has to pass as wholly as possible through the secondary air nozzle 2. When the secondary air nozzle 2 is directed upward or downward, however, the clearance 12 is established, as shown in FIGS. 5(b) and 5(c), between the furnace side end portion of the windbox 5 and the windbox side end portion of the secondary air nozzle 2. As a result, a portion of the combustion auxiliary air bypasses the secondary air nozzle 2 from that clearance 12 and leaks into the furnace, causing a problem in that the combustion auxiliary air does not make an effective contribution to combustion.